This report summarises the results from an investigation into the accuracy of condition assessment of electrical contacts via thermography measurements in the field. The investigation was carried out in Ludvika, Sweden at the Swedish Transmission Research Institute (STRI) outdoor test site during the autumn of 2007. The investigation was performed as a part of the PhD project Modelling of power equipment reliability with special reference to the impact of maintenance carried out at the RCAM research group at the KTH School of Electrical Engineering.
Two naturally aged disconnector poles of the make ABB NSA 400/3150 was loaded up to their nominal load in three stages and the contact temperature rises were measured both using thermography and thermocouples attached to the contacts. The thermography measurements were carried out by am experienced technician from Vattenfall Service. After the first set of measurements some contacts were subjected to standard maintenance and the measurements were repeated.
The investigation resulted in statistical distribution for the errors related to the estimation of contact temperature rise at nominal load based on thermography measurements. These error distributions were used to simulate the accuracy of the estimations. Furthermore the investigation resulted in two linear regression models of the relationship between contact resistance and temperature rise as well as the effect of maintenance on contact temperature rise.
A conclusion from the measurements was that statistical models should be used to estimate the effect of maintenance on the contact condition as well as estimating the contact condition from resistance measurements.
2008. , 26 p.